These days, cancer treatment using particle beams is known in which protons or heavy ions such as carbon ions are accelerated to about 70% of the velocity of light and are delivered with surgical precision onto the focus of a refractory cancer. While performing cancer treatment using particle beams, based on the treatment program implemented prior to the treatment, the positioning of the treatment table on which the patient is made to lie down is determined in such a way that the affected area is present at the irradiation position of the particle beams. As compared to the X rays used in radiation therapy, the dose of particle beams becomes higher in the deeper portion of the body (particle beams have the Bragg peak). Hence, as compared to the radiation therapy, the cancer treatment using particle beams can be performed with a smaller number of times of irradiation. Moreover, near the surface of the body, the dose of particle beams having the Bragg peak is smaller. Hence, in the cancer treatment using particle beams, the irradiation with particle beams can be done for a plurality of number of times while avoiding skin burn.
The tissues in the body, such as lungs or liver, perform cyclic movement attributed to the effect of respiration and cardiac motion. Such movement of the body tissues differs from person to person. Not only that, in the same person too, the movement of the body tissues changes every day, every week, or every year.
For that reason, in the conventional cancer treatment using particle beams, irradiation with the particle beams is done at the timing of switching between expiration and inhalation, which is the timing at which the movement and the shape of the affected area undergoes only a small change in synchronization with the respiration cycle (gating irradiation method). That is, in the gating irradiation method, the affected area is irradiated with particle beams at the timings in between expiration and inhalation.
However, in the gating irradiation method, since the irradiation with the particle beams are done only at the timings in between expiration and inhalation, the irradiation with the particle beam becomes intermittent in nature. For that reason, in the gating irradiation method, the treatment time becomes longer.